replaced mean on dimensions 2,3 by adaptive_avg_pooling2d  (#1838)
replaced mean on dimensions 2,3 by adaptive_avg_pooling2d  (#1838)

* replaced mean on dimensions 2,3 by adaptive_avg_pooling2d with destination of 1, to remove hardcoded dimension ordering

* replaced reshape command by torch.squeeze after global_avg_pool2d, which is cleaner

* reshape rather than squeeze for BS=1

* remove import torch

pytorch/vision,pytorch/vision,pytorch/vision,pytorch/vision,pytorch/vision,pytorch/vision